The majority of colorectal adenomas arise from adenomatous polyps and the most effective method for colorectal cancer prevention is through endoscopic removal of these lesions. The epidemiology of advanced neoplasia (advanced adenomas or cancers) in populations undergoing colonoscopic surveillance is not understood. Since occurrence of advanced neoplasia following polypectomy is low, a large, prospective study with high follow-up rates is needed to identify factors that predict these outcomes. The goal of this research is to identify factors that place individuals at high or low risk for development of advanced neoplasms after colonoscopic polypectomy by pooling individual data from eight completed adenoma studies. This effort will result in a cohort of approximately 10,000 individuals who underwent colonoscopic removal of all visualized polyps and were prospectively followed by undergoing one or more surveillance colonoscopies. Three specific aims were identified: 1) to determine the rate of occurrence of advanced neoplasms among individuals who undergo removal of one or more histologically verified adenoma(s); 2) to identify risk factors independently associated with occurrence of advanced colorectal neoplasms during colonoscopic surveillance; and 3) to identify characteristics of the baseline colonoscopy examination in patients with colorectal cancer discovered during the surveillance period. Current surveillance guidelines for individuals undergoing polypectomy are based on sparse data. Refinement of these guidelines requires a large, prospectively followed, well-characterized population, such as that resulting form the combined efforts of the present proposal. Results of this research are extremely timely and could have a major national public health impact. Given that data were collected through the conduct of the studies, this results in a cost-effective and highly efficient approach for assessing this important research area.